The present invention relates to methods and devices for coupling an antenna to plural receivers, and more particularly to a method and device for providing two filtered radio frequency (RF) output signals of selectable signal strength to two radio receivers from a single RF input signal received on an antenna.
An RF input signal received on an antenna may be provided to a waveguide for transmission to a location where suitable connections to radio receivers can be made, typically with an antenna coupling unit (ACU). An ACU directs transmit and receive signals to and from an antenna, and typically includes microwave circulators and/or isolators, filters, a splitter (hybrid or coupler), and a switch. When an antenna feeds multiple receivers that are to be protected (redundant), the ACU splits the RF input signal and provides output signals to the receivers. The split may be equal (0 dB difference between the output signals) or unequal (for example, one output signal may be 7 dB less than the other).
However, the ACU causes an insertion loss that decreases the signal to noise ratio, thereby lowering system gain. The loss is especially noticeable in systems in which the ACU splits the output signals unequally, and it is an object of the present invention to significantly reduce insertion loss caused by the ACU, especially when compared to ACUs in which a separate splitter follows the filter. Several solutions to this problem have been attempted, but none has proven satisfactory. For example, some early ACUs were comprised principally of a waveguide with reasonably low loss, but these were large and costly. The splitter was a 3 dB hybrid that split the input into two equal strength signals that fed two receivers. The insertion loss of the hybrid splitter was high, on the order of 3 db for the split and 0.3 dB residual for the waveguide at 6 GHz (in addition to the filter loss). A compromise was to reduce the loss in one of the split signals at the expense of the other signal. The hybrid was replaced with a 1 and 7 dB coupler that had a 1.2 dB insertion loss for the main receiver and 7 dB insertion loss for the secondary receiver at 6 GHz (in addition to filter loss). This provided about a 2 dB improvement at one receiver, but the higher loss at the other receiver was not acceptable to many users. Consequently, users who wanted to have the ability to select whether a signal was to be equally split or whether it was to be provided with low loss to one receiver were forced to employ both a hybrid and a coupler.
In other systems in which small size was more important than insertion loss, the size of the ACU was reduced by using thin film technology for power splitting even though insertion loss actually increased. This was done by attaching a waveguide-to-coax transducer to the waveguide filter's output flange. A coax cable was installed between the transducer's output connector and the thin film splitter (hybrid or coupler). Costs were reduced by integrating the transducer into the end of the filter (beyond the filter's end cavity) by removing the waveguide flange. Length was shortened by the moving the transducer's coax SMA connector from outside the waveguide filter's end cavity and directly coupling the SMA to the filter's end cavity. A small reduction in insertion loss could be achieved by connecting the splitter directly to the waveguide filter's output SMA connector, eliminating the loss in the connecting cable. Thus, prior art systems either reduced insertion loss, but were large and costly, or were small, but increased insertion loss.
It is desirable to improve the capability of a device connecting the antenna to the radio receivers by providing a selectable split between the signal strengths of the output signals so that the device can be used in systems with an equal split, a predetermined split, or a variable split. It is further desirable to add the ability to filter an input signal in the waveguide.
Accordingly, it is an object of the present invention to provide a novel device and method for providing two output RF signals from a single input RF signal that obviates the problems of the prior art.
It is a further object of the present invention to provide a novel device and method for providing two output RF signals from a single input RF signal without a separate power splitter and the insertion loss attendant therewith.
It is yet a further object of the present invention to provide a novel device and method for providing two output RF signals from a single input RF signal in which connectors for the output signals are attached directly to the waveguide, thereby eliminating the splitter (hybrid or coupler).
It is still a further object of the present invention to provide a novel waveguide that filters an input signal and provides two filtered output signals of selectable signal strength.
It is another object of the present invention to provide a novel multiple output filter coupler and method for providing plural RF output signals from a single RF input signal, the coupler having an RF waveguide filter for receiving an RF input signal at one end and plural tunable connectors attached at its end cavity for providing plural filtered RF output signals.
It is yet another object of the present invention to provide a novel integrated filter coupler and method for providing two radio frequency (RF) output signals of selectable signal strength from a single RF input signal with a waveguide that has two tuning adjusters inserted into an end plate closing one end of the waveguide for selectably varying the signal strength of one RF output signal relative to the signal strength of the other RF output signal.
It is still another object of the present invention to provide a novel filter coupler in which the length of the filter is reduced by putting coax connectors in the waveguide filter's end cavity rather than using a coax-to-waveguide transition at the end of the end cavity.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.